In the past it has been common practice to carry a pack on a person's back. Backpacks are used in a variety of applications including carrying camping supplies, books and even babies. Just about any heavy object that must be carried has been carried in a back pack.
Backpacks typically are equipped with two shoulder straps. Typically the weight of the pack hangs from these two straps from the shoulders of the user. Suspending too much weight from the shoulders over an extended period has been shown to be detrimental to the back causing problems ranging from simple discomfort and fatigue to spinal compression, back pain and misalignment of the spine. The problem has been aggravated in recent years as young children have been carrying overweight book packs. It has been suggested that a child carry no more than 15% of their body weight on their back. Children from grade school through high school and the university are carrying far in excess of this amount.
It has been known practice to manufacture hiking back packs, baby carriers and some high end day packs with a waist belt built in. The waist belt allows a portion of the pack weight to be distributed to the hips of the wearer. This arrangement has advantages in that it avoids putting a portion of the load on the spine. Most day use packs and school back packs have no supporting waist belt at all. However, a waist belt has not been used in combination with a book pack where there is no frame, and a detachable waist belt has not been used in combination with a day pack, book bag or school back pack.